Conventional flow damper is described referring to FIG. 16.
A flow damper J1 in FIG. 16 is provided with: an approximately cylinder-shaped valve body J2 in which a fuel passage is formed; a piston J4 that is slidable in an axial direction along a piston slide hole J3 formed in the valve body J2; a spring J5 that urges the piston J4 to an upstream side of a fuel flow; and a stopper J6 that restricts a travel of the piston J4 to the upstream side.
In the piston J4 is formed an aperture path J7 that communicates an upstream side and a downstream side of the fuel passage. When any abnormal condition such as excessive fuel outflow occurs in the injector, a downstream flow amount increases to increase a pressure difference before and after the aperture path J7, and the piston J4 moves to the downstream side (injector side) to seat a valve portion J8 of the piston J4 on a valve seat J9 of the valve body J2. In this manner, the flow damper J1 stops the outflow of the high-pressure fuel when any malfunction occurs accidentally (refer to U.S. Pat. No. 6,357,415-B and its counterpart JP-3521811-B, for example).
The conventional flow damper J1 has the following issues.
(1) The valve body J2 is one to be fastened to a common rail body J10. The common rail body J10 accumulates high-pressure fuel, so that intimate contact surfaces of the valve body J2 and the common rail body J10 must be highly oil tight seal surfaces, and the valve body J2 is fastened to the common rail body J10 at a large axial force.
The valve body J2 is fastened to the common rail body J10 at a high strength, so that even a slight deviation in accuracy or shape of a seat surface can distort the valve body J2 in a rotational side at the large axial force.
The valve body J2 supports the piston J4 therein in a slidable state, therefore, if the valve body J2 is distorted by the above-described cause to deform the piston slide hole J3 radially inward, a slide clearance between the valve body J2 and the piston J4 decreases to spoil a slide motion of the piston J4.
In addition, the intimate contact surfaces of the valve body J2 and the common rail body J10 (or the stopper J6) require high work accuracy such as a high flatness, which is a cause of a cost increase.
(2) A female screw (a hole for inserting the valve body J2 thereinto) J11 of the common rail body J10 may have strain such as deformation by any kind of cause. Correspondingly, as shown in FIG. 16, a male screw J12 at a side of the valve body J2 is provided on an outer circumference of a direct slide range J2 in which the valve body J2 and the piston J4 are in direct slide contact with each other.
Thus, when the valve body J2 is fastened to the common rail body J10 at the large axial force, the strain that occurs in the female screw J11 of the common rail body J10 is transmitted via a screw-fastening portion to the valve body J2. As a result, the valve body J2 is distorted and the piston slide hole J3 is distorted, too.
In this manner, the distortion of the piston slide hole J3 spoils the slide motion of the piston J4.